I have been thinking about this a lot lately as well KESAthans. I have been in about 16 level 4 raids and rarely get past using my 3rd attacker in a group over 5. These first 3 attackers are all maxed out, which I would debate that this gets me the +2 extra balls to catch "the boss" which can be very useful. I'm not sure if I am correct in believing this is more useful that going through 4-6 at level 30.
If one is trying to solo as many raid bosses as possible than maybe 6 at level 30 is a much better use of dust?